1. Field of the Invention
The present invention relates to a radio frequency (RF) structure, and more particularly to an RF structure that comprises an optimum padset for wire bonding and a high performance inductor that includes relatively thick metal inductor wires, both of which are located atop the final interconnect level of an interconnect structure. The present invention also provides methods for fabricating such an RF structure.
2. Background of the Invention
In the semiconductor industry, digital and analog circuits, including complex microprocessors and operational amplifiers, have been successfully implemented in silicon-based integrated circuits (ICs). Such Si-based ICs typically include active devices such as, for example, bipolar transistors and field effect transistors (FETs), diodes, and passive devices, including resistors, capacitors, and inductors.
Attempts to miniaturize radio frequency (RF) circuits, however, remain a challenge. RF circuits are generally employed in cellular phones, wireless modems, PDAs, and other types of communication equipment. The miniaturization problem is a result of the difficulty in producing a good inductor in silicon technologies which is suitable for RF applications at widely used microwave frequencies from 900 MHz to 2.4 GHz.
Monolithic microwave integrated circuits (MMICs), which are rapidly outpacing discrete ICs in mobile wireless communication products, require high-Q (quality factor) passive components, such as inductors and capacitors, to be able to realize integrated filters and matching sections with small insertion losses.
The typical design of high performance semiconductor components for use in RF technologies generally employs a thick aluminum metal wire since the performance of inductors is closely related to the resistance of the metal wire, e.g., high metal resistance typically leads to slow inductors.
On the other hand, bonding between a gold wire and aluminum bond pads degrades significantly for thicker aluminum bond pads. With thicker aluminum bond pads, more aluminum atoms tend to diffuse into the gold wire leads causing the formation of voids (intermetallic formation) resulting in poor wire bond reliability. As an example, the lifetime specification using a high temperature ball shear reliability test standard of a gold wire bond to a 4 μm thick aluminum pad was granted (lowered) to 100 hours at 200° C. during SiGe dual metal technology qualification; compared to a normal wire bond standard of 200 hours at 200° C.
FIG. 1 illustrates a typical prior art RF structure 10 formed on a final insulating layer 12 of an interconnect structure (not specifically shown). The prior art RF structure 10 includes thick aluminum inductor wires 14 for high performance, high quality factor (Q) inductors and a thick aluminum bond pad 16.
In view of the current state of the art, there is a need for providing a new RF structure and methods for fabricating the same that resolve the aluminum to gold wire bonding reliability issues for high performance RF technologies.